The present invention relates to alarm arrangements, in particular for use in association with swimming pools.
Children, in particular infants, often fall into swimming pools with fatal consequences. This happens even when parents or other supervisors practically stand next to such children.
Various devices and arrangements have been suggested to avoid such senseless drowning of children. However, these systems often are complicated, very expensive, and some are not effective and suffer from other disadvantages.
U.S. Pat. No. 4,121,200 (Colmenero) discloses a swimming pool alarm system for activating an alarm indicator responsive to the presence of a person in a pool being monitored. The system includes a frequency selective detector responsive to water disturbance created by a person in a swimming pool. The detector enables a transmitter at poolside. A receiver remotely mounted with respect to the poolside transmitter responds to the transmissions therefrom activating the alarm indicator.
In U.S. Pat. No. 4,701,751 (Sackeft) there is disclosed an alarm system for a swimming pool which comprises the use of a height sensing apparatus employing fibre optics and a logic circuit whereby an interruption of a pair of different elevations of light paths is accepted and the alarm remains silent and the interruption of the lowest light path only is reflected sounding an alarm.
U.S. Pat. No. 5,049,859 (Arnell) describes a pool safety alarm system which includes a water-activated sonar transmitter adapted to be worn on the body of a non-swimmer for continuously transmitting low frequency audio signals upon immersion of the transmitter. An underwater microphone or hydrophone is located within the pool and is connected to a receiver circuit having a band pass filter connected to a monostable multivibrator for supplying signals to an alarm.
In U.S. Pat. No. 5,097,254 (Merrithew) there is described a swimmer protection and pool safety warning device comprising a portable sonic signal generating member worn by a swimmer in a pool, the signal generating member having a switch or similar device which is activated at a predetermined depth.
U.S. Pat. No. 5,144,285 (Gore) discloses a pulsed ultrasonic apparatus for monitoring a swimming pool and which includes a transmitter housing securable to a child and provides a swept frequency pulsed output from a transducer within the housing when an electrical circuit is completed by having a pair of tabs on the outside of the housing immersed in water. The output from the transducer is detected by a receiving hydrophone and the hydrophone is connected to receiver circuitry which provides an appropriate alarm signal.
In U.S. Pat. No. 5,274,607 (Bean) there is described a system for continuous echo analysis of a body of liquid, surrounded by walls of known dimension, for the presence of an object.
U.S. Pat. No. 5,369,623 (Zerangue) describes at least one transducer support immersed in a swimming pool. The transducer support has a plurality of transducer means mounted on the support which are capable of sending and receiving acoustic energy.
U.S. Pat. No. 5,486,814 (Quinones) discloses a swimming pool monitoring device which can be attached to a child to constantly transmit an electromagnetic radio wave of a desired frequency. The monitoring device contains a water submersion sensor, which will deactivate the transmitter upon submersion. Whenever transmissions from the monitoring device are interrupted, due to immersion or battery failure, a receiver will sense this condition and activate an alarm, which may be visual, audible, or a signal that is relayed to further remote wireless equipment such as a pager or telephone dialing equipment that is used to dial an emergency telephone number.
In U.S. Pat. No. 5,638,048 (Curry) a sonar, lidar, or radar system is disclosed which generates an alarm signal if a child enters a swimming pool when the system is enabled, and includes multiple safeguards against sounding false alarms due to wind-activated waves in the pool or self interference arising from multi-path propagation of sonar signals. An acoustic or electromagnetic receiver having a narrow bandwidth is employed to demodulate a composite signal spectrum produced by a target object such as a child and signals generated by wind-activated waves.
It is an object of the invention to suggest an alarm arrangement, which is relatively simple and economic, and which is capable of protecting children and other users against the dangers of falling into water.
According to the invention, an alarm arrangement for causing an alarm signal to be emitted in response to a person being monitored when entering a water zone, the arrangement including at least one transportable electronic transmitter unit and at least one electronic receiver unit, the arrangement being characterized thereby that the transportable electronic transmitter unit has attachment means for associating it with a user""s body, and a housing containing operatively connected electronic circuitry components, and having water activated electrical contacts outside the housing for causing energization of the electronic circuitry when coming into contact with water so as to emit a continuous operative ultra-sonic signal when such a person wearing the transmitter unit enters into water in a water zone being monitored; and the receiver unit having a housing containing operatively connected electronic circuitry components, and having water activated electrical contacts outside the housing for causing energization of the electronic circuitry when coming into contact with water, and being adapted to detect any operative signal at a preselected frequency from the transmitter unit when the transmitter unit comes into contact with water in the water zone being monitored, and the receiver unit being adapted thereupon to emit a suitable alarm signal.
The transmitter unit may include an electronic circuit including operatively connected together connection means for connection to a battery, an electronic switch, a crystal stabilised oscillator, an amplifier and a speaker.
The speaker may be a piezo element.
The transmitter unit may be adapted to emit an operative ultra-sonic signal at a frequency of about 32 kHz.
The receiving unit may include an electronic circuit including operatively connected together connection means for connection to a battery, an electronic switch, a voltage regulator, a voltage comparator, a micro-processor, an active band pass filter, two amplifiers, a phase lock loop, a microphone and a speaker.
The micro-processor may be adapted by a first step to conduct an initial battery check routine whereby the logic state of the voltage comparator is monitored so as to establish whether or not the battery is sufficiently charged and to cause an appropriate signal to be emitted by the speaker.
The micro-processor may be adapted as a second step to monitor the logic state of the electronic switch to establish whether or not the switch is closed.
The electronic switch of the receiver unit may be adapted to close when the electrical contacts located outside of the housing are bridged by way of water, and if not bridged by way of water in a predetermined period of time, to cause an appropriate signal to be emitted by the speaker.
The micro-processor as a third step may be adapted to monitor signals received by the microphone and on reception of an operative signal having a preselected frequency to generate an appropriate signal which is amplified by the amplifier and conveyed to the speaker for emitting an alarm signal.
The micro-processor may be adapted to calculate frequencies of all signals received and on reception of a pre-selected frequency to enter into the first monitoring mode whereby an appropriate signal is emitted by the speaker indicating a sufficiently charged battery and thereafter generating an appropriate signal which is amplified by the amplifier and conveyed to the speaker, which generates an audible alarm signal.
The housing of the transmitter unit may include a base, opposite side walls and a top; the housing defining a first chamber adapted to contain the electronic circuitry components, and further defining a second chamber adapted to removably locate the battery and being closable by way of a threaded nut forming one of the electrical contacts of the transmitter unit.
The housing of the receiver unit may include a hollow cylindrical body closed at one side by a base and closed at the other side by a lid, which is removably and sealingly attached to the cylindrical body by a threaded ring.
The housing may trap a volume of air once the lid is attached, the air rendering the housing to be floatable if placed in water in the water zone.